The present invention relates to a piezoelectric actuator, and more particularly to a hermetical sealing structure for an electrostrictive element.
Recently, piezoelectric actuators have become extremely promising mechanical driving elements as precision positioning devices for optical or magnetic disk heads, various kinds of optical devices, precision machine tools and the like. Since the mechanical displacement due to the piezoelectric effect is essentially extremely minute, a plurality of electrostrictive ceramic layers or piezoelectric ceramic layers are stacked with internal electrodes as disclosed in the U.S. Pat. No. 4,681,667 issued on a Jul. 21, 1987. The mechanical displacement may be further increased by using a mechanical amplification mechanism as is disclosed in the U.S. Pat. No. 4,570,095 issued on Feb. 11, 1986.
In a conventional electrostrictive element using silver based internal electrodes, migration easily takes place at exposed ends of the internal electrodes in a humid atmosphere, and thus causing a poor insulation characteristics. When a humidity test is given, there occur numerous cases of discharge generation from the side surface or the corner parts, creating a substantial obstacle to the yield and the reliability of the products.